The polymerizable organic matrix of dental resins, cements or composites consists above all of a mixture of monomers, initiator components, stabilizers and pigments (J. Viohl, K. Dermann, D. Quast, S. Venz, Die Chemie zahnärztlicher Füllungskunststoffe [The chemistry of dental filling plastics], Carl Hanser Verlag, Munich-Vienna 1986, 21-27). As resins, mixtures of dimethacrylates are usually used (cf. A. Peutzfeldt, Resin composites in dentistry: the monomer systems, Eur. J. Oral. Sci. 105 (1997) 97-116; J. W. Nicolson, H. M. Anstice, The chemistry of modern dental filling materials, J. Chem Ed. 76 (1999) 1497-1501; J. W. Stansburry, Curing dental resins and composites by photopolymerization, J. Esthet. Dent., 12 (2000) 300-308; N. Moszner, T. Hirt, New Polymer-Chemical Developments in Clinical Dental Polymer Materials: Enamel-Dentin Adhesives and Restorative Composites, J. Polym. Sci. Part A: Polym. Chem. 50 (2012) 4369-4402).
A main disadvantage of the methacrylates used is that the polymerization thereof is accompanied by a volume contraction, so-called polymerization shrinkage. In the case of dental materials, polymerization shrinkage can lead, among other things, to disadvantageous shrinkage stresses and to marginal gap formation in filling composites, to reduced substrate adhesion in fixing composites or coating materials and to the dimensional stability of prosthesis plastics being impaired. In this connection, radically polymerizable cyclic monomers have attracted great interest in the preparation of dental materials due to the considerably lower polymerization shrinkage compared with linear monomers, such as e.g. methacrylates (cf. R. K. Sadhir, R. M. Luck, Expanding Monomers, CRC Press, Boca Raton etc. 1992).
Vinylcyclopropanes are characterized, compared with other known ring-opening monomers such as methylene-group-containing spiroorthocarbonates (SOC), spiroorthoesters (SOE) or bicyclic orthoesters (BOE), by the fact that the vinylcyclopropyl (VCP) group is not moisture-sensitive and in that, when it is radically polymerized, polymers with high molar masses are obtained which only contain hydrolytically stable C—C bonds in the main chain (N. Moszner, F. Zeuner, T. Völkel, V. Rheinberger, Macromol. Chem. Phys. 200 (1999) 2173).
From DE 198 12 888 A1, vinylcyclopropane derivatives and in particular vinylcyclopropane (meth)acrylates are known which can be copolymerized with acrylates and methacrylates.
Moreover, vinylcyclopropanes with several polymerizable groups are known. F. Sanda, T. Takata, T. Endo, Macromolecules 27 (1994) 3986, describe 1-vinyl-5,7-dioxaspiro[2.5]octan-6-one, a hybrid monomer which contains a vinylcyclopropane group and a cyclic carbonate group, and T. Okazaki, F. Sanda, T. Endo, Macromolecules 28 (1995) 6026, describe 1,10-bis(vinyl)-4,8,12,15-tetraoxatrispiro-[2.2.2.2.2.2]pentadecane, a monomer in which two vinylcyclopropane groups are joined to each other via a hydrolysis-sensitive spiroacetal unit. These compounds do not have an improved radical copolymerizability with (meth)acrylic compounds in comparison with monofunctional vinylcyclopropanes.
EP 0 798 286 A1 relates to multifunctional vinylcyclopropane derivatives with two to six vinylcyclopropane groups which enable the preparation of crosslinked polymers.
Using the example of the radical copolymerization of 1,1-bis(ethoxycarbonyl)-2-vinylcyclopropane with methyl methacrylate (MMA), it could be shown (F. Sanda, T. Takata, T. Endo, Macromolecules, (1994) 3982) that, compared with methacrylates, vinylcyclopropanes are characterized by a lower radical polymerizability, which considerably restricts their practical use. It is particularly disadvantageous that the known 1,1-bis(alkoxycarbonyl)-2-vinylcyclopropanes which are easy to obtain have a low photopolymerization activity.
EP 1 413 569 A1 discloses dental materials based on bicyclic cyclopropane derivatives such as e.g. 2-[bicyclo[3.1.0]hex-1-yl]acrylic acid methyl ester, which exhibit an improved reactivity on radical polymerization (N. Moszner, F. Zeuner, U. K. Fischer, V. Rheinberger, A. de Meijere, V. Bagutski, Macromol. Rapid. Commun. 24 (2003) 269). However, these more reactive monofunctional bicyclic cyclopropyl acrylates can only be obtained with great difficulty.